Ink cartridges for supplying ink to recording devices are broadly used. One type has a case that holds a porous member impregnated with ink. Another type includes a flexible bag filled with ink. A variety of configurations have been provided in the ink cartridges to enable detection of the amount of ink remaining in the ink cartridge.
JP-B-3-60670 discloses an ink cartridge with a plate-shaped member that abuts the outer surface of a flexible bag that is filled with ink. Movement of the member is detected to detect the amount of residual ink in the bag.
JP-A-3-505999 discloses an ink cartridge including a case with one open surface. The open end of the case is covered with a flexible film. Ink is contained in the space between the case and the flexible film. An electric contact is disposed at the bottom of an opening in the case. The film moves toward the electric contact as ink is used up during printing operations. When the film contacts the electric contact, the electric contact is activated to indicate that ink has run out.
An ink-jet printer is known, in which ink is discharged from nozzles to recording paper to perform printing. Such an inkjet printer is generally provided with a detachable ink cartridge. When an inkjet head is driven to perform the discharge operation in a state in which the ink cartridge is empty, air sometimes invades the inkjet head. An inkjet head into which the air has been introduced may be damaged so as to be inoperable. Therefore, it is necessary to detect the amount of the ink stored in an ink cartridge. A method for detecting the amount of the ink is known in which an amount of the ink is detected by estimating and accumulating amounts of the ink used each time printing is performed. However, errors tend to arise in such calculations. Therefore, it is prudent to stop the use of the ink cartridge before actually necessary. As a result, ink is wasted.
An alternative technique has been proposed (see, e.g., JP-A-9-001819, FIG. 7). That is, a float, which has a specific gravity smaller than that of ink, is arranged on the ink contained in the ink cartridge. The height of the float floating on the ink is detected from the outside to detect the amount of the ink contained in the ink cartridge.
However, according to the technique disclosed in JP-A-9-001819, the float sometimes sticks to the wall surface. That is, the float does not descend due to disturbances such as surface tension of ink adhered to an inner wall surface of the ink cartridge. Therefore, it is impossible to indicate the correct amount of the ink contained in the ink cartridge.